I had a customer update their Magento install and after got reports that chrome users couldn’t log in some times. I found a post that point me in the right direction after spreading a while researching the issue.

The trick was to create the directory app/code/local/Mage/Customer/Model and copy the file Session.php from app/code/core/Mage/Customer/Mode into it.

Then comment out $this->renewSession(); from the setCustomerAsLoggedIn Function.